[Deproteinization of the influenza virus by infected cells at 4 degrees C]

The process of influenza virus deproteinization was compared in two systems: chick fibroblasts infected with fowl plague virus (FPV) and MDCK cells infected with WSN virus. The cells were infected with 3H-uridine-labeled viruses. Deproteinization of virus structures was studied at 4 degrees C and after incubation of virus-infected cells at 37 degrees C. At 4 degrees C, the bulk of radioactivity of the original virus was found in the perinuclear cytoplasm (the fraction obtained by treatment of triton X-100-purified nuclei with 0.1 M citric acid) and much less radioactivity was found in the nucleus. After incubation at 37 degrees C the level of radioactivity in the nucleus increased and reached or even exceeded that in the perinuclear cytoplasm. A biophysical analysis of the structures showed the perinuclear cytoplasm to contain subviral particles (SVP) similar to nucleoids as well as RNP with a buoyant density of 1.35 g/ml in cesium chloride. The nuclear extract contained RNP with a buoyant density 1.39-1.41 m/ml. The experimental results indicate that the first stage of deproteinization of virus particles to SVP occurs at 4 degrees C. The second stage of deproteinization, to RNP with a buoyant density 1.35 g/ml, also occurs at a low temperature.